Current natural gas reserves are often situated far from world markets. Although it is possible to transport the natural gas, in many cases it is preferred to convert the natural gas fields in situ into more readily transportable products such as synthetic fuels, methanol or dimethyl ether. The conversion processes generally consume very large amounts of oxygen and produce excess steam. Background for this field is to be found in “Oxygen Facilities for Synthetic Fuel Projects”, by W. J. Scharle et al., Journal of Engineering for Industry, November 1981, Vol 103, pp. 409-417, in “Fundamentals of Gas to Liquids” January 2003, The Petroleum Economist Ltd, and in EP-A-0748763.
It is not always possible to construct an air separation unit close to the site of the conversion process, for example for environmental or economic reasons. In this case, the steam generated is sent via a pipeline to the air separation unit site and there it is expanded in a turbine coupled to the main compressor of the air separation unit.
However, the cost of such steam pipelines is prohibitive since the steam has to be maintained at a high temperature to prevent condensation.
In some cases, there may be a number of processes, each producing excess energy in the form of steam or another hot gas. There may be insufficient energy available on the site of the process to justify exporting that energy and the steam or other hot gas may be vented to the atmosphere. Furthermore, the individual processes may each produce a different grade of steam, such that the two grades of steam cannot be sent to a single steam turbine.